Investigation Of Fabrication, Structure And Properties Of Carbon Nanotube Reinforced Aluminum Matrix Composites

2024Al matrix composites reinforced with 0~4.2vol.% carbon nanotubes (CNTs) were fabricated by powder metallurgy technique. The purification of CNTs, uniformly dispersion of CNTs among alloy powders, the thermal stability of CNTs and Al and the densification of the composites were systemically investigated and analyzed. By using SEM, TEM, XRD, XPS, HRTEM, DSC, tensile test and hardness test techniques, the microstructure, the mechanical properties and the processing parameters of the composites were examined and optimized. In addition, the effects of the microstructure on the overall mechanical properties were related.The investigation of the effect of refluence time on CNTs in nitric acid showed that the aspect ratio, the ratio of hybridizable C atom of sp2 and sp3 and surfacial defects of CNTs reduce, meanwhile, the functional groups containing oxygen element increase when refluence time increases. The dispersion of CNTs after refluence is better than that of CNTs before refluence, and dispersing ability increases with refluence time increasing. CNTs can homogenously distributed on the surface of alloy powders when the content of CNTs is less than 2.1vol.% with mechanical stirring assisting ultrasonic shaker. However, CNTs form conglobations when content is 4.2vol.%. The mechanisms of the purification and dispersion of CNTs, the dispersion of CNTs among alloy powders were discussed based on surfacial structure of CNTs and alloy powders.The study of thermal stability of CNTs in Al matrix indicated that CNTs and Al react and form nano-Al4C3 phases with needle shape when the temperature is above the melting of alloy aluminum. The activation energy of the reacton between CNTs and Al is 194.01 kJ/mol, which is higher than that of graphite and Al. Moreover, the interface of Al4C3 phases and Al matrix keep directly atom bonding, and bond tightly. It also were found that an orientation relationship of (200) Al //(00012)Al C exists between Al4C3 phases and Al matrix. The reaction mechanisms of CNTs and Al matrix were taken over by HRTEM and XPs analysis. The grain size of composites is finer than that of the matrix materials after hot extrusion, so CNTs can restrain the growth of Al grains in compoises, and fine the Al grains. Moreover, CNTs were very stabile in the present fabrication method, and mainly distributes on the grains boundary and inner-grains of the composite matrix. The interfaces of CNTs and Al matrix are very clean and straight. CNTs and Al matrix keep directly atom bonding, and exist (200) Al //(101? 1)CNTs orientation relationship.CNTs content affected significantly the mechanical properties of the composites. The hardness, tensile strength, Young's modulus and yield strength of the composites firstly increase and then reduce with CNTs content increasing. The hardness, tensile strength, Young's modulus and yield strength reache the maximum value, 136.2 kg/mm2,521.7 MPa,92.2 GPa and 497.7 MPa respectively, when CNTs content is 2.1vol.%. They are increased 33.0%,34.6%,20.8% and 39.7% in relation to the matrix during the same fabrication. The fracture manners involves the bridging, the pull-out and pulling to rupture, and the length of CNTs pulled out is very short, when small amount of CNTs were added to Al matrix, however, the pull out and debonding took placed in the composite with larger amount of CNTs, and the length of CNTs pulled out is very longer in relation to that of 2.1vol.% CNT composite. The strengthening mechanisms of CNTs reinforced metal matrix composites were discussed according to the microstructure and mechanical properties of the composites...